Usage: srvctl upgrade model -s <source-version> -d <destination-version> -p {first|last} [-e <name>=<value>[,<name>=<value>, ...]
-s <source-version> Version from which to upgrade
-d <destination-version> Version to which to upgrade
-p {first|last} Whether the command is called from the first upgraded node or the last upgraded node
-e <name>=<value>[,<name>=<value>, ...] Additional name value pairs for upgrade
-h Print usage

In general thsi should only be needed during an CRS upgrade, as part of root.sh script. Nevertheless, as it's there it should be documented. Especially the -e parameter seems to be worth more information than the -h docu provides.